<!DOCTYPE html>
<html lang='en'>
<head>
    <meta charset='UTF-8'>
    <title>下文规则 5 - 1</title>
</head>
<body>
    <script>
        let obj = {
            a: 1,
            b: 2,
            fun: function () {
                console.log(this.a + this.b);
            }
        };

        var a = 3;
        var b = 4;

        setTimeout(obj.fun, 2000);  // 7（3 + 4）；定时器内调用函数，适用规则 5
    </script>
</body>
</html>
